Chapter 6 What is Variable and Types with Program Explain in Details.

 What is Variable in JAVA ?

• It is a storage space which is used to store data just like a container or box.
• It's value may be changed.
• It always contains last value stored to it.
• It is always declared with data type.

For Example Variable Declaration 

int rollno;

float marks;

char grade;

• Here:- rollno is a variable of type int, marks is a variable of type float and grade is a variable of type char.

Variable Initialization

• We can initialize a variable at the time of declaration of variable or after declaration.

int rollno=201;

float marks=97.77;

char grade='A';

• Here :- 201 is the value of rollno,85.6 is the value of marks and A is the value of grade. Character value is always written in single quotes.

Other method of variable Initialization

• We can also initialize a variable after the time of declaration of variable.

int rollno;

float marks;

char grade;

rollno=201;

marks=85.6;

grade='A';

Rules to define a variable

• The first letter of a variable should be alphabet or underscore(_).
• The first letter of variable should not be digit.
• After first character it may be combination of alphabets and digits.
• Back spaces are not allowed in variable name.
• Variable name should not be a keyword.

Types of Variable

• Local Variable
• Instance Variable
• Static Variable

Local Variable:- 

• A variable declared inside the body of the method or constructor or block is called local variable.
• Local variable can be used only inside that method/function in which it is declared.
• A local variable can be a static variable.

//Q1. Sum Of Two variable

class Tech369kk

{

 public void add()

 {

 int x, y=10,z=20;    //declaring local variable

 x=y+z;

 System.out.println("Add="+x);

 }

 public static void main(String[] args)

 {

  Tech369kk obj=new Tech369kk();

  obj.add();      

 }

}

                        ******Output:***** Add= 30

Instance Variable:- 

• A variable which is declared inside a class but outside the body of the method or constructor or block is called instance variable.
• Instance variable can be used anywhere in the program.

class Easy

{

 //these instance variabe can be used

 int x,y=30,z=20;

 public void add()

 {

 x=y+z;//accessing instance variable

 System.out.println("Add="+x);

 }

 public void sub()

 {

 x=y-z;//accessing instance variable

 System.out.println("Sub="+x);

 }

 public void mul()

 {

 x=y*z;//accessing instance variable

 System.out.println("Mul="+x);

 }

 public static void main(String[] args)

 {

  Easy obj=new Easy();

  obj.add();  

  obj.sub();

  obj.mul();

 }

}

******Output:*****

Add= 30

Sub= 10

Mul= 600

                                                

Static Variable:- 

• A variable which is declared with static keyword, inside a class but outside the body of the method or constructor or block is called static variable.
• Static variable is stored in the static memory for permanently.
• Static variables are created when the program starts and destroyed when the program stops.
• Static variable can be called by class name directly.

// Q3. find static keywords in java

class Statt

{

 //declaring static variable

 static String text="I Hope Clear your Doubts in Java Variable.";

 public static void main(String[] args)

 {

     System.out.println(Statt.text);

 }

}

******Output:*****

I Hope Clear your Doubts in Java Variable